security: allow finer granularity in permitting copy-up of security xattrs

Copying up xattrs is solely based on the security xattr name. For finer
granularity add a dentry parameter to the security_inode_copy_up_xattr
hook definition, allowing decisions to be based on the xattr content as
well.

Co-developed-by: Mimi Zohar <[email protected]>
Signed-off-by: Stefan Berger <[email protected]>
Acked-by: Amir Goldstein <[email protected]>
Acked-by: Paul Moore <[email protected]> (LSM,SELinux)
Signed-off-by: Mimi Zohar <[email protected]>

Author: stefanberger

fs/overlayfs/copy_up.c

@@ -114,7 +114,7 @@ int ovl_copy_xattr(struct super_block *sb, const struct path *oldpath, struct de
 		if (ovl_is_private_xattr(sb, name))
 			continue;
 
-		error = security_inode_copy_up_xattr(name);
+		error = security_inode_copy_up_xattr(old, name);
 		if (error < 0 && error != -EOPNOTSUPP)
 			break;
 		if (error == 1) {

include/linux/lsm_hook_defs.h

@@ -176,7 +176,8 @@ LSM_HOOK(int, 0, inode_listsecurity, struct inode *inode, char *buffer,
 	 size_t buffer_size)
 LSM_HOOK(void, LSM_RET_VOID, inode_getsecid, struct inode *inode, u32 *secid)
 LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
-LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, const char *name)
+LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, struct dentry *src,
+	 const char *name)
 LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
 	 struct kernfs_node *kn)
 LSM_HOOK(int, 0, file_permission, struct file *file, int mask)

include/linux/security.h

@@ -398,7 +398,7 @@ int security_inode_setsecurity(struct inode *inode, const char *name, const void
 int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
 void security_inode_getsecid(struct inode *inode, u32 *secid);
 int security_inode_copy_up(struct dentry *src, struct cred **new);
-int security_inode_copy_up_xattr(const char *name);
+int security_inode_copy_up_xattr(struct dentry *src, const char *name);
 int security_kernfs_init_security(struct kernfs_node *kn_dir,
 				  struct kernfs_node *kn);
 int security_file_permission(struct file *file, int mask);
@@ -1016,7 +1016,7 @@ static inline int security_kernfs_init_security(struct kernfs_node *kn_dir,
 	return 0;
 }
 
-static inline int security_inode_copy_up_xattr(const char *name)
+static inline int security_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
 	return -EOPNOTSUPP;
 }

security/integrity/evm/evm_main.c

@@ -946,7 +946,7 @@ static void evm_inode_post_setattr(struct mnt_idmap *idmap,
 		evm_update_evmxattr(dentry, NULL, NULL, 0);
 }
 
-static int evm_inode_copy_up_xattr(const char *name)
+static int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
 	if (strcmp(name, XATTR_NAME_EVM) == 0)
 		return 1; /* Discard */

security/security.c

@@ -2628,6 +2628,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
 
 /**
  * security_inode_copy_up_xattr() - Filter xattrs in an overlayfs copy-up op
+ * @src: union dentry of copy-up file
  * @name: xattr name
  *
  * Filter the xattrs being copied up when a unioned file is copied up from a
@@ -2638,7 +2639,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
  *         if the security module does not know about attribute, or a negative
  *         error code to abort the copy up.
  */
-int security_inode_copy_up_xattr(const char *name)
+int security_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
 	int rc;
 
@@ -2647,7 +2648,7 @@ int security_inode_copy_up_xattr(const char *name)
 	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
 	 * any other error code in case of an error.
 	 */
-	rc = call_int_hook(inode_copy_up_xattr, name);
+	rc = call_int_hook(inode_copy_up_xattr, src, name);
 	if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
 		return rc;
 

security/selinux/hooks.c

@@ -3530,7 +3530,7 @@ static int selinux_inode_copy_up(struct dentry *src, struct cred **new)
 	return 0;
 }
 
-static int selinux_inode_copy_up_xattr(const char *name)
+static int selinux_inode_copy_up_xattr(struct dentry *dentry, const char *name)
 {
 	/* The copy_up hook above sets the initial context on an inode, but we
 	 * don't then want to overwrite it by blindly copying all the lower

security/smack/smack_lsm.c

@@ -4885,7 +4885,7 @@ static int smack_inode_copy_up(struct dentry *dentry, struct cred **new)
 	return 0;
 }
 
-static int smack_inode_copy_up_xattr(const char *name)
+static int smack_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
 	/*
 	 * Return 1 if this is the smack access Smack attribute.